Biochar kiln

ABSTRACT

A biochar kiln is disclosed. An example of the biochar kiln includes a body having a one-piece rolled wall, a curved floor attached to the sidewall by a single weld line, and a removable lid. The example biochar kiln includes a plurality of semi-independent combustion cells. The example biochar kiln also includes a ventilation subsystem, an ember suppression subsystem, and a stack subsystem. A control subsystem may configured to monitor a plurality of zones of the biochar kiln for a plurality of process control variables, to produce a quality biochar product with well-managed emissions.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of U.S. Provisional PatentApplication No. 62/317,573 filed Apr. 3, 2016 for “Biochar Kiln,” herebyincorporated by reference in its entirety as though fully set forthherein.

BACKGROUND

Biochar is made from biomass (trees, agricultural waste, etc.) in anoxygen deprived, high temperature environment. Quality biochar has highpurity, absorptivity and cation exchange capacity. This can providesignificant benefits to several large markets including, but not limitedto, agriculture, pollution remediation, odor sequestration, separationof gases, and oil and gas clean up.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an example biochar kiln.

FIG. 2 is an interior view of a floor of the example biochar kiln,illustrating a ventilation subsystem.

FIG. 3 is a close-up view of the ventilation subsystem shown in FIG. 2.

FIG. 4 is another close-up view of the ventilation subsystem shown inFIG. 2.

FIGS. 5-8 are close-up views of the exterior of the example biocharkiln, illustrating the ventilation subsystem.

FIGS. 9-10 are perspective views of example components of an embersuppression subsystem of the biochar kiln.

FIG. 11 is a perspective view of an example stack subsystem of thebiochar kiln.

FIG. 12 is a high-level block diagram of an example control subsystem ofthe biochar kiln.

FIG. 13-23 are illustrations of example insulation of the biochar kilnshown in FIG. 1.

DETAILED DESCRIPTION

A biochar kiln is disclosed, including construction of the kiln andvarious subsystems such as, but not limited to, ventilation, stack,control, insulation, and ember suppression. The kiln may be implementedto produce biochar.

In an example, the kiln is configured for internal combustion and heatgeneration as needed, to convert biomass into biochar. During operation,the kiln may experience frequent and wide thermal cycling. For example,every 2 days, the kiln temperatures can vary between −30 and +1300degrees Fahrenheit (e.g., stack temperature ranges from −30 F to 1850F).

The biochar kiln is configured to support slow pyrolysis and canaccommodate a number of variables. Variables include, but are notlimited to, a “green” and/or dry feedstock, large and/or small pieces ofthe feedstock, various and multiple different species of the feedstock,and operation according to variable processing times. The biochar kilnis robust in that it may be operated under a number of variableoperating conditions, while still producing a consistent and highquality biochar product.

The biochar kiln may include a local and dedicated process controlsystem. The control system may be implemented with a ventilationsubsystem, an ember suppression subsystem, and airflow management or“stack” subsystem, to help ensure high quality and high yield biochar isproduced while simultaneously complying with emissions standards.

In an example, the biochar kiln has multi-zone combustion cells that arecomputer-controlled to maintain target temperatures while creatingfaster burns. Multi-zone servo dampers are computer-control to manageinlet air flows to the combustion cells to support optimum heating. Thebiochar kiln may also have removable stacks and a stack hole sealingmechanism. The kiln may also be configured for negative flue gaspressure to eliminate fugitive emissions.

Before continuing, it is noted that as used herein, the terms “includes”and “including” mean, but is not limited to, “includes” or “including”and “includes at least” or “including at least.” The term “based on”means “based on” and “based at least in part on.”

FIG. 1 is a perspective view of an example biochar kiln 10. The biocharkiln 10 may include a main body portion 12 and a lid 14. The main bodyportion 12 is configured to receive a feedstock (not shown) by removingthe lid 14 and loading the feedstock before replacing the lid 14. In anexample, the biochar kiln further includes a base portion 16. The baseportion 16 may be configured such that it is raised off of the ground.This enables airflow under the main body portion 12. A ring 18 may alsobe implemented to lift the biochar kiln 10, e.g., using a loadertractor, forklift or other suitable machinery.

In an example, the kiln wall 20 may be made of a one-piece, rolled wall.Body welds, where needed (e.g., between the floor 222 and wall 20, andvarious ports), are made on curved surfaces to lower structural andthermal stress to those joints.

The floor 24 may also be a one-piece heavy gauge, high strength steel.The floor 24 may be downward elliptical-shaped (the shape being visiblein FIG. 1 and FIG. 5) to withstand heavy falling wood chunks duringfilling. The surface of the floor 24 is curved and has only one weldjoint along the perimeter where it joins with the wall 20. The floor 20and walls 20 may anneal with use, which also serves to relieve stress.

Before continuing, it should be noted that the examples described aboveare provided for purposes of illustration, and are not intended to belimiting. Other devices and/or device configurations may be utilized tocarry out the operations described herein.

FIG. 2 is an interior view of a floor 20 of the example biochar kiln 10,illustrating a ventilation subsystem 24. The ventilation subsystem 24may include a plurality of semi-independent combustion cells 25 a-g. Inthe example shown, there is a combustion cell 25 g in the center, andsix combustion cells 25 a-f between the center cell 25 g and the kilnwall 20. An outside vent pipe 28 a-f leads to the center of each cell toprovide combustion air. FIG. 3 is a close-up view of the ventilationsubsystem 24 shown in FIG. 2. FIG. 4 is another close-up view of theventilation subsystem 24 shown in FIG. 2.

In an example, upward facing thermowell tubes 26 a-g may be built intothe floor 20 for each combustion cell 25 a-f. The thermowell tubes 26a-f may be positioned adjacent vent pipes or air inlets 28 a-f. Anotherthermowell tube 26 g may be positioned substantially in the center ofthe floor 20, e.g., for combustion cell 25 g. The thermowell tubes 26a-g may be configured with monitors to enable interior biochartemperature sensing while the biochar is cooking.

FIGS. 5-8 are close-up views of the exterior of the example biocharkiln, illustrating a ventilation subsystem 30. The ventilation subsystem30 includes ports 32 around the perimeter of the body 12 of the biocharkiln 10. Each of the ports 32 is connected to the internal air inlets 28a-f. These ports may be closed (e.g., as shown in FIG. 5) and openedmanually, or via computer control.

In FIGS. 6-8, an automatic control is shown including dampers 34 withair inlet 36 which can be connected to a gas line 38 to a main line 40to supply ignition gas into the chamber formed in the body 12 of thebiochar kiln 10.

The dampers 34 are each attached to the outside portion of thecorresponding vent pipes 28 a-f to provide computer-controlled airflow.Each damper has a servo-controlled butterfly valve 42 to regulateairflow. Damper airflow results from negative pressure in the kiln (thevacuum sucks air in), or can be blown in by an external blower or both.

In an example, the ventilation subsystem 30 may be implemented with thecontrol system described herein to provide a controlled airflow, thusenabling a carefully controlled burn and emissions control. In anexample, each servo is computer-controlled and provides physicalposition feedback to the computer to confirm the valve's position. Thefeedback enables the computer control to determine whether a valve isworking, blocked or failed. In an example, servo accuracy is about+/−0.5 degrees to permit precise control.

In an example, the kiln is equipped with one or more pressuretransducer(s) to insure negative kiln pressure. Air vent pipes for eachcombustion cell may also pass through the floor flange. After a burn,the vent pipes can be sealed with cam-lock caps to help cut off oxygen,stop combustion and cool the biochar.

At the end of a burn, dampers 34 are removed from the vent pipe openings32 and replaced with airtight, gasket cam-lock caps 33 (shown in FIG. 4)over the vent pipe openings 32. The dampers 34 are then temporallysecured to the kiln wall during kiln transit or moved to another kilnfor further use.

Damper wiring may be routed to a kiln-mounted control board to eliminatethe need to unplug and plug damper wiring when the kiln travels to andfrom the workstations.

In addition to airflow control, the damper assembly 34 provides acomputer-controlled gas-start system to ignite the wood during a freshburn. Gas flow is turned by the computer via a gas solenoid.

During operation gas is piped into the assembly where it flows through aventuri pulling in air to the air/gas mix tube before being exposed to apreheated glow plug igniter. The ignited gas then travels by athermocouple probe to verify its ignition and down the vent pipe tostart the wood fire at its combustion cell.

FIGS. 9-10 are perspective views of example components 46 and 48 of anember suppression subsystem 44 of the biochar kiln 10. An embersuppression subsystem 44 is provided in the event ember suppression isneeded after a burn. In an example, a gas 46 (e.g., nitrogen, carbondioxide, and/or other inert gases) can be injected into the kiln 10(e.g., at one or more ports 32, the exhaust stack 51, or other suitablelocation) to purge and/or dilute residual oxygen in the chamber of kiln10. In an example, carbon dioxide is utilized because it is about twotimes heavier than air, which enables the biochar to flood a kiln fromthe bottom up so it can be processed the next morning. Without oxygen,there is no combustion and the embers are put out (stop burning) toallow the biochar to cool down.

The introduction of suppression gases can be managed by a regulator 48(FIG. 10) at port 32 or other suitable location, to maintain a low,positive kiln pressure. This helps keep fresh air from entering thekiln. After the heat is reduced to a safe level, the control system canturn off the gas supply. In an example, a safe temperature is about 300F to 400 F (e.g., it is noted that the auto ignition temperature of woodis about 570 F). By using suppression gases, instead of a water quench,the biochar can be processed in its dry state.

The ember suppression subsystem may also be implemented at least in partin the lid. In an example, the lid has a gasket attached to it at theperimeter. The gasket gets squeezed between lid flange located above thegasket and the flange on the kiln rim below. The gasket reduces orprevents air leaks during ember suppression. During the burn, the gasketalso helps retain fugitive smoke in the kiln (e.g., in case of a shortterm negative pressure drop).

FIG. 11 is a perspective view of an example stack subsystem 50 of thebiochar kiln 10. In FIG. 11, a portion of the stack 51 (shown in FIG. 1)is illustrated in detail. In an example, a stack 51 sits on top of thelid 14 of the biochar kiln 10.

In an example, a reflector/flow director is attached to the underside ofthe lid. This reflects radiant heat back into the kiln and biochar whilealso directing the flue gas to the out perimeter of the kiln, whichimproves heat distribution in the kiln.

The stack may be anchored by gravity and/or other attachment(s). In anexample, the base of the stack is wide enough to provide stability(e.g., up to about 90 mph wind loads). At the bottom of the stack 51, asmoke chamber 52 funnels kiln gases into the stack 50. A stack blower 54moves the smoke first horizontally and then curves straight up andthrough the top of the stack 51.

During example operation, the stack blower 54 moves combustion airthrough the duct 52 where the smoke then enters a venturi mix tube. Airfrom the blower 54 entrains nearby flue gas to pull it up into the mixtube of the stack 51. At the top end of the mix tube (see FIG. 1), theair and flue gas combine on their way to a secondary or exhaust burner(not shown).

As the air and flue gas pass through the burner (natural gas orpropane), it ignites volatile gases (if any), which lowers emissionpollution, burns particulates, heats the vapors and spirals the smokeupward to heat refractory material above the burner. The spiral effectis cause by vanes placed just after the burner. The spiraling hot vaporsspend more time heating the refractory than a straight upward flow.

In an example, the target refractory temperature is about 1650 F, and ismanaged by adjusting the burner fuel flow rate and/or the blower flowrate. At 1650 F, CO combines with radical Oxygen to make CO2, which isan acceptable emission gas (whereas CO is highly regulated). Inaddition, at 1650 F, thermal NOX is also kept low.

An added stack extension (not shown) may be provided to help increaseflow rate due to stronger convection flow. Less entrainment air isrequired, for less cooling, less use of burner gas. This may reduce oreliminate the need for refractory material, thus reducing cost.

The blower 54 provides a negative kiln pressure (e.g., by reducing oraltogether eliminating fugitive smoke, and providing suction to pull airin from the dampers). The blower 54 also provides oxygen for emissionconversion and burner combustion, and helps control stack temperaturesby adding cooling air.

FIG. 12 is a high-level block diagram of an example control subsystem 56of the biochar kiln 10. The control subsystem 56 may include one or morecontroller 58. In an example, the controller 58 may be implemented as aPLC (programmable logic array). The controller 58 may be mounted in anysuitable location (e.g., on a pole near the kiln). The PLC has enoughcomputing power to run multiple kilns. In an example, the cable betweenthe kiln and the PLC has 4 conductors (2 for DC power and 2 for data)which make plugging and unplugging easy. In another example, acontroller 58 may be provided for each kiln where and can travel withthe kiln.

The controller 58 may receive input and/or feedback from the kiln (e.g.,the ventilation subsystem 24, the ember suppression subsystem 44, and/orthe stack subsystem 50). The controller 58 may also provide output orcontrol of the various subsystems.

In addition, the kiln and stack may also be considered to include aplurality of control zones 60. The control zones 60 are independent,horizontal and/or vertical zones within the kiln body 12 and stack 51.The zones each have one or more process control variable (e.g.,temperature, oxygen level). The zones 60 may be physical component(s)and/or area(s) (both physical and virtual) of the kiln body 12 and/orstack 14 itself, and/or a process component, such as the feedstock,product (including intermediary product), air, gas(es), and smoke withinthe kiln body 12 and/or stack 14.

Examples zones 60 include, but are not limited to, floor combustioncells, the kiln feedstock itself, the produced biochar itself, the kilnlid 14, the stack smoke chamber, stack mix venturi, the stack burner,Flue gas spiral vanes, Stack refractory, Stack extension. The zones 60may be equipped with one or more sensor and/or dampers. These zones 60may be managed by the controller 58.

In an example, each kiln 10 has its own computer control board (e.g.,for easy transit and improved individual kiln reliability). The controlboard may be wirelessly linked to a site controller to accept site-wideremote commands (e.g., fire start), to provide archive data and to sendstatus alarms.

To integrate multiple zones across multiple kilns 10, and/or multiplezones within a single kiln 10, the control subsystem 56 can apply one ormore group state machines on top of individual zone state machines toinsure even burns across individual zones. For example, group statemachines may include a program to ask individual zones to stop atintermediate temperatures to permit slower zones to catch up. When allzones arrive at the temperature, the group is then released to continuethe process.

The control board may be accessed via tablet, smart phone, and laptopdevices, e.g., which provide the user interface and control. The controlboard may also control work lights and strobe alarms at the site and/orindividual kiln(s).

In an example, the controller 58 implements state machine software anddevice controllers to independently manage each of the varioussubsystems (e.g., 24, 44, and 50) and zones 60 (e.g., a floor combustioncell). To integrate zones 60, the controller 58 can be implemented asone or more group state machines on top of individual state machines toensure optimal group performance (e.g., to ensure consistent or evenburns across all cells).

The controller 58 may enable non-programmers to develop advanced controllogic and algorithms without making changes to its lower level programcode. Unique control instructions (e.g., “recipes”) can be generated forunique customer needs, feedstock type, emissions requirements, biocharattributes, etc.

In an example, the control subsystem 56 provides higher yields, higherbiochar quality, greater consistency, optimized flow rates, vaporpressure control, end of cycle detection, lower emissions and shorterburn cycles. By way of illustration, each floor combustion cell may beprovided with an optimal amount of combustion air for maximumtemperature rise while working to reach a preset temperature goal. Theburn control can use Boolean logic and/or PID (proportional, integraland derivative) control or other techniques for fastest temperatureattainment.

FIG. 13-23 are illustrations of example insulation of the biochar kiln10 shown in FIG. 1. On cold, windy days, over 80% of the kiln's heat canbe lost through the steel shell (e.g., lid 14, walls 20, and floor 22)of the biochar kiln 10. On a windless, warm day, heat loss can be under30%. If the kiln is insulated with a ceramic blanket (or other types),heat loss can be reduced by as much as 95%. When insulation is used,internal temperatures climb more quickly for shorter burn times, yieldimprovement (less wood burned), reduced emissions (less wood burned),improved consistency (soak heats are more evenly distributed), andimproved quality. Exposing the ceramic blanket to rain and snow quicklytransforms it into a poor insulator. To protect the blanket, it may beencapsulated in a high temperature weatherproof skin.

In an example, a cylindrical insulator 62 (FIG. 13) is provided thatfollows the shape of the kiln wall 20. FIG. 14 is a close up of theupper side edge of the wall 20 showing the cylindrical insulator 62 indetail.

In another example, the insulating cylinder 62′ may stand away from thekiln wall 20 to allow forced airflow through a gap between the kiln wall20 and the insulating cylinder 62, and optionally through openings orvents 64 (e.g., after a burn). In an example, (not shown), a ring orband with similar sized and spaced openings can be fit snugly to theinsulation. During processing, the band can be rotated so that the vents62 are at least partially or fully covered. To aid in cooling, the bandcan be rotated so that openings in the ring line up with the vents 64.By natural convection, the air inside the space is heated by the Kilnwall. It then rises out the vent openings, drawing cool air into the airspace from the bottom.

Ambient air (or chilled air) blowers may be provided to force air topass between the kiln wall and insulation for cooling before it exits onthe far side. Sensing the existing air temperature and internalthermowell temperatures can indicate when the kiln is safe to open.

In an example, the insulation is about 1.5 inches thick, although othersizes may be provided. The insulator 62 and 62′ can detach from the kilnto permit replacement and maintenance as needed.

There may be provided a clearance between a gripper ring 66 and thebottom of the insulation so that gripping the gripper ring 66 (e.g.,with a forklift or other machinery to raise/lower the kiln 10) does notpinch or otherwise harm the insulation. This distance may depend on thedimensions of the gripper and the expected accuracy of the loader driverwhile picking up the Kiln.

The insulation 62 and 62′ holds significantly more heat inside the Kilnduring processing, and is expected to reduce the amount of wood burned(increasing efficiency) with increased yield of char.

If using natural convection doesn't allow cooling of the Kiln in a shortenough time, forced convection may be provided. One way to accomplishforced convection is by mounting a pipe 68 vertically to the kiln 10, asshown in FIG. 17. The pipe 68 can direct air into the space between thekiln wall 20 and the insulation. It may be possible to leave this pipe68 uncapped during processing, since little air will escape. If desired,the pipe(s) 68 can be capped.

The pipe(s) 68 distribute forced air both ways (e.g., left and right)into the air space on one side of the kiln 10. If it is desired to“collect” the air on the opposite side of the kiln 10, another similarpipe can be installed. If faster cooling is desired, 4 pipes can beused, 2 for inlet and 2 for “exhaust”, though the complexity increasessignificantly. These are only exemplary configurations. Otherconfigurations are also contemplated.

As shown in FIGS. 18-19, plenum walls 70 may be provided inside the airspace to keep the cooling coverage more even than if the forced aircould flow vertically inside the air space. These plenum walls 70 may bewelded to the Kiln wall in a circular direction and could be full orpartial walls.

FIG. 20 shows a blower 72 attached to the inlet of the forced airsystem. Forced convection possibly will require an additional blower foreach kiln 10 in the cool-down cycle.

FIG. 21 shows how to use the “waste” heat from the kilns 10. If theheated air from cooling a processed kiln 10 is piped into the inlet airpipes of a waiting kiln 10′, some amount of drying of the wood might beaccomplished while waiting to process the loaded kiln. This may reducethe time needed to evaporate all the moisture in the wood duringprocessing.

The heated air may be forced into 2 or 3 inlets, as illustrated by FIG.21. Or a manifold of sorts could be attached to the waiting kiln, wherehot air could enter all air inlets and would exit through the lid (someventing mechanism might be provided on the lid if general air leaks arenot enough).

FIGS. 22-23 show a kiln 10″ having six 2×2 inch legs (legs 74 a-d arevisible in FIG. 22) and a rolled angle bottom with top insulation 76 andbottom insulation 78. Bottom insulation 78 may not be provided if thebottom area is enclosed with insulation or insulation sections 78.

In this example, there may be no air blown into/out of the bottom forcooling to reduce the need for plumbing through the insulation 80. Asthe heat rises, and when the walls and inside air were cooled, thebottom may lose heat to the Kiln air. If forced air cooling is desiredfor the bottom, a small diameter pipe may be attached to the blower, andcool air can be blown into the bottom chamber which exits from vents inthe bottom insulation sections.

A similar air space/insulation configuration may be used for the lid.The stack blower may be used to provide the forced air for cooling. Itmay implement a switched damper to divert the air from the stack to thelid and/or kiln. It is noted that the kiln and lid may be hot ifplumbing needs to be connected. In another example, a blower is attachedto the lid that is used for cooling.

In an example, the kiln insulation is provided in sections to make iteasier to install. Overlapped sheet metal joints may hold sectionstogether and help prevent air loss during cooling.

In an example, the kiln wall insulation is enclosed in a “box” (e.g., of1/16″ or 16-gauge (or thinner) sheet metal). For the kiln walls andbottom sections, these may be rolled to fit, with bent or welded endsfor fastening the “front” and “back” sides together. An attachmentmechanism/bracket may be welded to the kiln. In other examples, theseinsulation sections may be fastened to the brackets.

If the insulation section dimensions are about half or whole multiplesof about 14.5 inches, fiberglass rolls may fill the inside of theinsulation sections (e.g., 16 inch stud spacing less 1.5 inch stud isabout 14.5 inches). It is noted that careful dimensioning may lead tomore efficient use of the insulation.

It is noted that the examples shown and described are provided forpurposes of illustration and are not intended to be limiting. Stillother examples are also contemplated.

1. A biochar kiln, comprising: a body having a one-piece rolled wall, acurved floor attached to the sidewall by a single weld line, and aremovable lid; a ventilation subsystem; an ember suppression subsystem;a stack subsystem; and a control subsystem.
 2. The biochar kiln of claim1, further comprising a plurality of semi-independent combustion cells.3. The biochar kiln of claim 2, further comprising a center combustioncell is provided in a center of the body, and six perimeter combustioncells are provided between the center combustion cell and the wall. 4.The biochar kiln of claim 3, further comprising an outside vent pipeloading to a center of each of the perimeter combustion cells to providecombustion air.
 5. The biochar kiln of claim 2, further comprising aplurality of thermowell tubes built into the curved floor for each ofthe combustion cells.
 6. The biochar kiln of claim 5, wherein thethermowell tubes are positioned adjacent the vent pipes.
 7. The biocharkiln of claim 1, wherein the ventilation subsystem includes ports aroundthe perimeter of the body of the biochar kiln, each of the portsconnected to internal air inlets.
 8. The biochar kiln of claim 1,further comprising an automatic control including computer-controlleddampers to regulate airflow into the body of the biochar kiln.
 9. Thebiochar kiln of claim 8, wherein damper airflow is by negative pressurein the kiln or blown in by an external blower or both.
 10. The biocharkiln of claim 1, wherein the stack subsystem includes a stack blower tomove combustion air through a duct where smoke then enters a venturi mixtube.
 11. The biochar kiln of claim 10, wherein air from the blowerentrains nearby flue gas to pull up into the venture mix tube, and theair and flue gas combine en route a secondary burner.
 12. The biocharkiln of claim 1, wherein the ember suppression subsystem includes a gasinjected into the body of the biochar kiln to purge and/or diluteresidual oxygen in the body.
 13. The biochar kiln of claim 12, whereincarbon dioxide gas is utilized to enable produced biochar to flood thebody of the biochar kiln from bottom-up.
 14. The biochar kiln of claim1, wherein the control subsystem manages a plurality of zones within thebody.
 15. The biochar kiln of claim 14, wherein the zones includeindependent horizontal and vertical zones.
 16. The biochar kiln of claim14, wherein the zones include at least one of a plurality of floorcombustion cells.
 17. The biochar kiln of claim 14, wherein the zonesare managed for variable kiln wood, kiln biochar, stack smoke, stackmix, stack burner temperature, and flue gas.
 18. The biochar kiln ofclaim 14, wherein the zones are monitored by one or more sensor and/ordampers.
 19. A biochar kiln, comprising: a body having a one-piecerolled wall, a curved floor attached to the sidewall by a single weldline, and a removable lid; a plurality of semi-independent combustioncells; a ventilation subsystem; an ember suppression subsystem; a stacksubsystem; and a control subsystem configured to monitor a plurality ofzones within the body for a plurality of process control variables. 20.The biochar kiln of claim 19, further comprising a center combustioncell is provided in a center of the body, and six perimeter combustioncells are provided between the center combustion cell and the wall.